[Amps] R. MEASURES PRAYERS ANSWERED

[Peter Chadwick]

Rich said:
>1.  Pi-networks are never operated at resonance, they are operated  
close to resonance.  Low-pass Pi-networks resonate a bit lower than  
the operating freq and high-pass Pi-networks resonate above it.<
If it isn't resonant i.e. volts and amps are in phase, then you won't get maximum output and will likely get worse IMD. I am aware that the US Extra Class licence exam defines resonance as XL = XC, but this is only an approximation, and falls apart very badly when the working Q is low. If you use the only definition of resonance which holds up under all conditions i.e. the input impedance of the network is resistive (as far as the tube sees it - strays will have some effect if you calculate and compare with reality, especially on the higher bands), then the pi network is resonant. So is the L network, but if you use XL = XC, then both cases suggest that the circuit isn't resonant.
Operating into a non-resonant load leads to an elliptical load line - see Pappenfus et al.

73
Peter G3RZP